1. Field of the Invention
The present invention relates to lane boundary line recognition devices and computer-readable storage mediums for storing programs capable of recognizing lane boundary lines on a roadway on which an own vehicle drives, and assisting a driver of the own vehicle in order to perform driving safely.
2. Description of the Related Art
There has been proposed a driver assist technology capable of recognizing lane boundary lines on a roadway, on which an own vehicle drives, on the basis of images obtained by one or more in-vehicle cameras mounted on the own vehicle, and performing the driver assist of the own vehicle on the basis of the recognized lane boundary lines. The driver assist technology often provides warning regarding occurrence of abnormalities to the driver of the own vehicle, for example when the own vehicle departs from the own vehicle lane on the roadway on which the own vehicle drives. In order to provide the driver assist technology previously described, it is necessary to correctly detect and recognize the lane boundary lines of the own vehicle lane on the roadway, the presence of a branch road and a junction in front of the own vehicle. The branch road branches from the roadway on which the own vehicle drives. In general, the surface of the roadway is divided into one or more lanes such as vehicle lanes, a bike lane, a parking lane, and a sidewalk by using lane boundary lines, i.e. solid white lines, dotted white lines, etc. In order to provide the driver assist, there has been proposed a device capable of correctly detecting and recognizing the presence of a branch road, which branches from the roadway ahead the own vehicle.
For example, a patent document, Japanese patent laid open publication No. 2006-331389 discloses a lane boundary line recognition device capable of searching a surrounding area of previously-detected lane boundary lines, and detecting lane boundary lines on the roadway in currently-obtained image relating to the surrounding area. When a lane width between the detected lane boundary lines at both sides (the right side and the left side) of the own vehicle lane is out of a predetermined range, the lane boundary line recognition device determines that the lane boundary line candidate having a low parallel degree is a lane boundary line of a branch road which branches from the roadway ahead the own vehicle. By the way, the parallel degree is obtained by comparing an estimated travel route of the own vehicle with each of the detected lane boundary lines.
However, for the device disclosed in the patent document 1 previously described, it is necessary to calculate such a parallel degree between the estimated travel route of the own vehicle and each of the lane boundary lines, and detect the presence of a branch road on the basis of the calculated parallel degree. In other words, the device disclosed in the patent document 1 correctly judges the presence of a branch road only when a road width between the lane boundary lines of the roadway gently increases to meet the branch road.
On the other hand, it is difficult for the device disclosed in the patent document 1 to correctly recognize the presence of a branch road when a road width of the roadway suddenly expands at a junction in North America and Japan, and a junction point of a branch road in an urban area in Japan. This would cause a possible problem of it being difficult to correctly detect the presence of a branch road because the device often misses the lane boundary line which belongs to the branch road.